Long spar buoy structure and erection method



Filed May 9, 1966 1968 s. s. LOCKWOOD, JR.. ET AL 3,390,408

LONG SPAR BUOY STRUCTURE AND ERECTION METHOD 2 Sheets-Sheet 1 Armin H45July 2, 1968 5, og woon, JR" ET AL 3,390,408

LONG SPAR BUOY STRUCTURE AND ERECTION METHOD Filed May 9, 1966 2Sheets-Sheet 2 INVENTORS.

6mm; 6 Z My t/e fxm Wm w =z/ BY Mm M r United States Patent 3,390,408LONG SPAR BUOY STRUCTURE AND ERECTION METHOD George S. Lockwood, .lr.,Los Augeles, Thad Vreeland,

Jr., Arcadia, and Nick Koot, South Laguna, Calif assignors to GlobalMarine, Inc., Los Angeles, Calif., a corporation of Delaware Filed May9, 1966, Ser. No. 548,610 Claims. (Cl. 9-8) ABSTRACT OF THE DISCLOSURE Along spar buoy having an elongate, positively buoyant body which is manytimes greater in length than its maximum transverse dimension, in whichthe body is defined by a plurality of serially arranged body sectionsconnected together in moment-free connector means which isolate bendingmoments developed in any one section from the adjacent sections of thebody. The body sections have structures and buoyancy so related to eachother than the buoy floats freely with the sections disposed verticallyrelative to each other.

This invention relates to novel marine buoy structures of the type knownas long spar buoys. More particularly, it relates to an articulated longspar buoy and to a novel method for constructing and erecting such abuoy.

Proper instrumentation of the ocean is a major problem in acquiringreliable data regarding the ocean and its Weather. Such data is requiredfor military purposes, such as for improving or predicting sonarperformance, as well as for commercial purposes, such as locatingundersea mining and farming areas and for predicting optimum shippingroutes. Ideally, the oceanographic instrument platform or vehicle shouldbe relatively motionless even in a severe sea, rugged, and low in cost.Also, the platform should be moorable without the use of complex andexpensive mooring systems.

Long spar buoys have been proposed for use as instrument platforms inoceanographic instrumentation projects; such buoys preferably arefabricated of a number of sealed lengths of oil well drill pipe or oilwell casing pipe and are of substantially constant diameter over theirlengths. A long spar buoy may have a length of several thousand feet, ifdesired. Such buoys are ideally suited for use in oceanographic researchsince they have very little heave even in extremely high seas and areinexpensive in comparison with more conventional surface buoys.Originally, it was proposed that the adjacent pipe lengths in such along spar buoy be rigidly connected together.

The construction of a rigid long spar buoy requires the use of highlyskilled personnel and complex equipment, and such a buoy must beassembled in a vertically progressive manner at its intended location ofuse if the imposition of damaging bending moments in the buoy is to beavoided. Also, it has been found that wind and wave action upon theupper end of a rigid long spar buoy and the action of ocean currentsupon other portions of a rigid long spar buoy combine to producesignificant bending moments in the buoy. Such moments cause the materialon the convex side of the buoy to be placed in tension and the materialon the opposite concave side of the buoy to be placed under compression.Since a long spar buoy usually is not constrained from rotating by itsmooring structure, the buoy is free to rotate even while subject tobending moments. Therefore, the loads developed in the buoy by imposedbending moments vary cyclically at a rate corresponding to the rate atwhich the buoy rotates. Where the buoy is rigid or substantially rigidover its entire length, these loads, whether "ice static or cyclic,produce undesirably large stresses in the buoy; the cyclic nature ofthese stresses is even more undesirable because they rapidly lead tofatigue fractures in the buoy.

.This invention provides an articulated long spar buoy useful inoceanographic instrumentation projects. The articulation of the buoysignificantly reduces the bending moments which may be imposed upon thebuoy. The buoy, therefore, is not subjected to the stress levels whichwould be encountered in a rigid long spar buoy of the same length anddiameter. The invention also provides a novel method for constructingand erecting such a buoy without the use of specially trained personnelor complex and costly equipment.

Generally speaking, this invention provides along spar buoy whichincludes an elongate, positively buoyant body having a length many timesgreater than its maximum transverse dimension. The body is comprised ofa plurality of substantially identical tubular members arranged inend-to-end relation to define a plurality of serially arranged buoy bodysections. Moment-free connectors are provided between adjacent bodysections for positively interconnecting the body sections and forisolating from one section any bending moments developed in an adjacentsection. Preferably, the moment-free connectors are double universaljoints.

In terms of procedure, this invention provides a method for fabricatingand erecting a long spar buoy. The method includes the step offabricating a long spar buoy Without ballast on shore in a substantiallyhorizontal attitude from a plurality of substantially identical lengthsof pipe or the like, the body of the buoy being articulated at selectedlocations along its length. The method also includes the step of towingthe unballasted fabricated buoy body to a desired location at sea by atowing vessel. The method also includes the steps of ballasting at leasta selected one of the pipe lengths adjacent the intended lower end ofthe buoy so that said end of the buoy sinks until the buoy is submergedto the extent desired and the buoy is disposed in a substantiallyvertical position.

The above-mentioned and other features of the present invention are morefully set forth in the following detailed description of presentlypreferred embodiments of the invention, which description is presentedwith reference to the accompanying drawings, wherein:

FIG. 1 is an elevation view of a long spar buoy;

FIG. 2 is an enlarged cross-sectional elevation view of a portion of thebuoy shown in FIG. 1;

FIG. 3 is an elevation view illustrating an initial step in a method offabricating and erecting the long spar buoy shown in FIG. 1; and

FIGS. 4, 5 and 6 show successive steps in the method illustrated in FIG.3.

A surface-piercing, positively buoyant long spar buoy 10 is shown inFIG. 1, floating vertically in a body of water 11 having a free surface12. The buoy has an elongate substantially hollow body 13 comprised ofan indeterminate number of similar elongate tubular elements 14.Preferably, the tubular elements are defined by convenient lengths, say20 to 40 foot lengths, of oil well drill pipe or oil well casing pipe ofselected diameter. The buoy, when in place at sea, has an upper section15 which extends through water surface 12; buoy section 15 is shown tobe defined by a number of pipe Sections which have a diameter greaterthan the pipe sections used in the remainder of the buoy. It will beunderstood, however, that the upper section of a buoy according to thisinvention may have a diameter the equal to or less than the remainingsections of the buoy Without departing from the scope of the invention.All of the pipe lengths in the upper section of the buoy are rigidlyinterconnected in endto-end relation by means of pipe coupling collars16. The ends of the pipe lengths in the upper section of the buoy aswell as in the other buoy sections are preferably welded to each othervia welding collars. Alternatively, the ends of the pipe lengths may beaccurately machined to define precision threads which are screwed intosimilar threads machined on the interior surface of a threaded couplingcollar. When threaded couplings are used, an epoxy thread-sealingcompound preferably is applied to the threads just before the joints aremade up; the compound cures in the assembled joints. As a result, thejoints between adjacent pipe lengths are made up watertight.

The lower end of buoy upper section is connected to a second buoysection 17 by a moment-free connector 18 shown in more detail in FIG. 2.Buoy section 17 is rigid along its length. The remainder of the lengthof the buoy is defined by an indefinite number of rigid sections 19,each comprised of a number of pipe lengths rigidly connected together.Buoy sections 17 and 19 are serially interconnected by additionalmoment-free connectors 18.

As shown in FIG. 2, the lowermost pipe length in upper buoy section 15carries a conical end fitting 20 secured to the pipe length by athreaded pipe collar 16. The upper end of second buoy section 17 carriesa similar conical fitting 20. Moment-free connector 18 is comprised of adouble universal joint 21 connected between the adjacent end fittingsalong the axis of the buoy. The relatively movable parts of the doubleuniversal joint are housed within a protective rubber sleeve 22. Theopposite ends of the double universal joint define stub shafts 23 whichare welded to the opposing end fittings. The opposite ends of the rubbersleeve are bonded to the adjacent stub shafts close to the end fittings.The double universal joints permit the adjacent sections of the buoy tomove pivotally relative to each other in response to dilferentiallateral loads on the adjacent body sections. The body sections can movein any desired direction about a point intermediate the sections andlying on the axis of the buoy. The joints, however, prevent the adjacentbuoy sections from moving axially relative to each other. If desired,lengths of woven wire cable or swivels, for example, may be used asmoment-free connectors in accord with this invention.

An access platform 25 is mounted to the upper end of upper buoy section15 above water surface 12 and mounts a radio antenna 26. The antenna iscoupled to a suitable transmitter, not shown, located within the buoyadjacent the platform for transmission of radio signals to a remotereceiving station. A plurality of oceanographic instrument transducers27 are strapped to the buoy at selected locations along its length. Ifdesired, however, and if compatible with the nature of a giventransducer, the transducers may be located within the buoy. Thetransducers preferably provide electrical output signals which areapplied to the radio transmitter via a suitable cable 28 extending alongthe length of the buoy and secured at desired locations to the buoy bysuitable straps 29.

As shown in FIG. 2, a bulkhead plate 30 is disposed across each pipelength used in the construction of the buoy adjacent each of its ends.Each bulkhead plate is welded about its periphery to the interior of theadjacent pipe length to provide a watertight seal across the interior ofthe pipe length. In the event that the connection between the adjacentend of the pipe length and the next pipe length (or the connectionbetween the pipe length and a conical end fitting) should leak, the sealprovided by the bulkhead plate holds flooding of the buoy to a minimum.

A long spar buoy may have a length of from about 100 or 3000 feet ormore. The pipe lengths from which the buoy is constructed may havediameters of from 4 to 24 inches. Where the buoy is of considerablelength, the lower portions of the buoy are fabricated from strongersections of pipe than are used for the upper portions of the buoy. Thispractice is followed so that the weight of the buoy is kept as low aspossible, yet the buoy is sufficiently strong at all points along itslength to withstand the external water pressures which tend to crush thehollow buoy body. The lower end of the buoy carries a mooring ring 31 towhich a mooring cable 32 is secured for mooring the buoy at a desiredlocation in body of water 11.

The upper section of buoy 10 must be sufficiently long that this sectionof the buoy, together with any payload carried by it, has positivebuoyancy when the section is vertically disposed and a selected portionof its length (preferably about 25 feet) lies above water surface 12.The positive buoyancy of the upper section of the buoy may be slightrelative to the total buoyancy of the buoy; preferably, however, theupper section of the buoy is the most buoyant section of the buoy. Forthe reasons set forth below, it is desired that the uppermost section ofthe buoy not be unduly long, but it is desired that the uppermostsection be as long as possible in order that its angular motion beminimized. Therefore, in order that the length of buoy section 15 may beheld within workable limits, it is preferred that the pipe lengths usedin the fabrication of buoy section 15 be of greater outer diameter thanthe pipe lengths which are used in the fabrication of the remainder ofthe buoy.

A floating long spar buoy is subjected to lateral loadings at its upperend by wind and wave related forces. Particularly where the buoy is ofextreme length, the lower reaches of the buoy are subjected totransverse shear loads when the buoy extends through a region ofrelatively fast moving water into a region of relatively slow movingwater. If the buoy were essentially rigid throughout its entire length,these lateral loadings upon the buoy would produce a sizable bendingmoment in the buoy. Mooring loads also contribute to the bending momentimposed on the buoy. Because the buoy has a relatively small diameter,the fiber stresses in the pipe lengths used in the construction of arigid buoy could readily possibly exceed the yield strength of thematerials used in constructing the buoy unless the pipe sections weremade of special steel or provided with substantial wall thickness. Theuse of special alloys in the construction of the buoy is to be avoided,however, in order that the cost of the buoy may be held as low aspossible. The use of pipe sections having thick wall sections isincompatible with large buoy payload capacity. Moreover, assuming thatthe buoy is rigid along its length, the buoy is free to rotate withinthe sea unless complex and costly mooring systems are used to preventrotation. If the buoy is free to rotate while being subjected to a givenbending load, the fiber stresses in the buoy body vary cyclically.Cyclic loads and the stresses associated therewith, even of relativelysmall orders of magnitude, particularly when superimposed on largestatic loads, are to be avoided to the greatest extent possible. Cyclicstresses at levels below the yield stress of the material are known tocause metals and other materials to fracture from fatigue. Superimposedupon the static and dynamic bending stresses are the fiber stresseswhich are produced by the hydrostatic crushing loads imposed upon thebuoy; these stresses increase with water depth.

The pivotal interconnection of buoy sections 15, 17 and 19 bymoment-free connectors 18 prevents the buoy from being subjected tolarge bending moments over its length. As a result, the maximum stresspresent in the pipe lengths from which the buoy is made is maintainedwellbelow the stress corresponding to the yield point of the pipe metal.Furthermore, any bending moments which may be imposed upon any givensection of the buoy between a pair of universal joints is maintained ata low level and cyclic variations in these moments are likewise held toinconsequential levels. As a result, the useful life of the buoy isextended since fatigue is minimized.

The use of moment-free connectors in buoy 10 also substantiallyeliminates electrolytic corrosion related to stress. It is known thatsteel, when disposed in an electrolyte such that it forms one electrodeof a galvanic cell, corrodes fastest where the stress in the steel isgreatest. By minimizing the stress levels in the buoy by use of themoment-free connections between adjacent buoy sections, deterioration ofthe buoy by corrosion is less than in an equivalent rigid buoy.

The use of the moment-free universal joint couplings in buoy at selectedlocations along its length permits the buoy to be fabricated and erectedeasily and economically by the procedure illustrated in FIGS. 36. Eachbuoy section 15, 17 or 19 is assembled on a slightly inclined waystructure located on shore immediately adjacent body of water 11. Thebody sections are made up as previously described to the desired lengthfrom pipe lengths 14 of the desired diameter and wall thickness. Eachbody section is fitted with a conical end fitting 20. Instrumenttransducers are mounted to each section as required and each bodysection is assembled free of ballast. As each pipe length is added, thebody section is moved down the way structure toward water 11. No givenbody section is launched from the way structure until it has beenconnected via a moment-free coupling 18 to the adjacent end of the nextbody section. Thus the construction of the buoy progresses from one endof the buoy to the other.

After the fabrication of the buoy body is complete, the buoy, with theplatform structure in place, is towed by a tow vessel 36 to the sitewhere the buoy is to be moored, as shown in FIG. 4. If desired,auxiliary flotation or buoyancy chambers 37 are strapped to theunballasted buoy so the buoy floats on water surface 12 during thetowing process. At the location where the buoy is to be moored, a cable38 is connected from the buoy mooring ring to the tow vessel via a winch39 mounted on the vessel; this cable may be the same cable used to towthe buoy to the mooring location from the initial fabrication site.Also, as shown in FIG. 5, mooring cable 32 is connected to the mooringring and extends from the floating unballasted buoy to an anchordisposed on the bottom of body of water 11.

The buoy body sections at and adjacent the intended lower end of thebuoy are then filled with ballast as required. The buoy may be ballastedby flooding selected pipe lengths with water or by filling selected pipelengths with concrete, sand, steel shot or the like; the use ofconcrete, sand or steel shot as ballast is preferred since such ballastmaterial, as opposed to water, produces a more effective regulation ofbuoy center of gravity because of its greater density. The auxiliarybuoyancy tanks, if fitted, are then removed before cable 38 is payed outfrom the tow vessel. The ballasted buoy then assumes a configurationresembling a catenary between the end of cable 38 and the positivelybuoyant buoy sections at and adjacent the upper end of the buoy, asshown in FIG. 5. Such a catenary configuration of the buoy causes noharm to the buoy, however, since the articulated construction of thebuoy prevents appreciable bending moments from developing along thelength of the buoy; the same stress-free conditions within the buoy arealso obtained as the buoy is being towed from the on-shore constructionsite to the location where the buoy is to be used, even though the buoymay be towed through heavy seas.

The next step in the process of erecting the fabricated buoy is shown inFIG. 6, i.e., paying out cable 38 from tow vessel 36 to lower theballasted end of the buoy downwardly of the vessel through water 11.This procedure is carried out gradually so that the descent of the lowerend of the buoy is controlled at all times. If the buoy were merely castoif from the tow vessel, the buoy would plummet downwardly and becometotally sub-' merged before it assumed a stable position after bobbingvertically for some time. Such motion of the buoy, especially where thelength of the buoy is great, would impose severe dynamic loads upon thebuoy, and particularly upon the moment-free connections, such that themoment-free connections may part or become permanently damaged.Moreover, the upper sections of the buoy would tend to whip through theWater so fast that the transducers carried by the buoy would be severelydamaged. Impact between the upper section of the buoy and the tow vesselwould also be likely.

After the buoy has been lowered to the point where it floats verticallyin a stable manner and does not bob, cable 38 is disconnected from thebuoy. The radio antenna and the radio transmitter may then be installedin the erected buoy to complete the buoy fabrication and installationprocedure. If desired, the removal of cable 38 from the buoy may bedelayed until after the antenna and transmitter have been installed. Thebuoy is then ready for use as an exceptionally stable, rugged andinexpensive oceanographic and meteorological instrumentation station.

Once the buoy has reached its intended location of use, the buoy can beerected and rendered operational within one working day.

The above-described method of fabricating and erecting a long spar buoyhaving the length contemplated by this invention is possible only wherethe buoy is articulated at several locations spaced along the length ofthe buoy. If the buoy were substantially rigid along its length, buoyconstruction would have to be carried out at the site where the buoy isto be moored. Such construction would require the use of a speciallyequipped vessel, such as a workboat fitted with a crane, similar tovessels now in use for drilling oil wells and the like at sea. A rigidbuoy would have to be assembled in a vertical attitude. Onceconstruction of a rigid buoy is commenced, it should proceed withoutinterruption until the buoy body is completely assembled. Where the buoyis of great length and the construction time is long, the probability ofa change in the weather at the construction site is increased. If thevessel is subjected to adverse weather, it must either ride out thestorm with all its hazards, or alternatively, the partially completedbuoy could be left in place, supported by auxiliary buoyancy members,while the construction vessel retreats to a safe place to wait out thestorm. In either case, valuable time is lost. Further, specially trainedpersonnel are required for on-site construction of a rigid long sparbuoy. The above-described articulated long spar buoy structure andconstruction method inherently avoids many if not all of these handicapsattendant to rigid buoys. Economic construction and installation of thearticulated long spar buoy is not dependent upon the existence ofrelatively long periods of fair Weather and smooth seas at the intendedlocation of the buoy.

Certain structural arrangements and procedural sequences relating tothis invention have been described above merely by way of example infurtherance of a complete and comprehensive explanation of theinvention. It will be realized that these examples do not encompass allforms which this invention may take, although they do suggest and teachthat the structures and procedures described may -be altered or modifiedWithout departing from the scope of the invention. Accordingly, theforegoing description is not to be regarded as limiting the scope ofthis invention.

What is claimed is:

1. A long spar buoy comprising an elongate positively buoyant bodyhaving a length many times greater than its maximum transversedimension, the body being comprised of a plurality of tubular membersarranged in end-to-end relation to define a lesser plurality of seriallyarranged buoy body sections, and moment-free connector means connectingadjacent body sections for isolating bending moments developed in onesection from the adjacent sections, the body sections beingcooperatively configured and arranged in structure and buoyancy so thatthe body floats freely with the body sections disposed vertically ofeach other.

2. A long spar buoy according to claim 1 wherein each moment-freeconnector means includes a universal joint connected between theproximate ends of each two adjacent body sections.

3. A long spar buoy according to claim 2 wherein each universal joint isa double universal joint.

4. A long spar buoy according to claim 2 wherein the relatively movableparts of each universal joint are sealed Within a flexible watertightsheath.

5. A long spar buoy according to claim 2 wherein each body sectionadjacent a universal joint carries a conical end fitting to which oneend of the adjacent universal joint is mounted.

6. The method of fabricating and erecting a long spar buoy comprisingthe steps of fabricating on shore an unballasted buoyant buoy bodyhaving a slenderness ratio of at least about fifty-to-one and includingthe installation at selected locations along the length of the buoy ofarticulation means between adjacent sections of the body of the buoyeach of which has a length substantially greater than its diameter sothat bending moments developed in one section are isolated from thesections adjacent to the one section, towing the unballasted buoyantbuoy body to a desired location at sea by a tow vessel, at leastpartially filling at least a selected one of the buoy body sectionsadjacent the intended lower end of the buoy with ballast, and sinkingthe lower end of the buoy downwardly of the tow vessel until the buoy issubmerged to the desired eXtent and the body sections are substantiallyaligned with each other in a substantially vertical relation.

7. The method according to claim 6 including the step, performed at thedesired location at sea, of connecting to b the lower end of the buoy amooring cable prior to sinking the lower end of the buoy.

8. The method according to claim 6 including the step, performed at thedesired location at sea, of securing a cable from the tow vessel to theintended lower end of the buoy before ballasting the buoy, the sinkingprocedure being accomplished by paying the cable out from the tow vesselto lower the lower end of the buoy.

9. The method according to claim 8 wherein the lower end of the buoy islowered at a rate substantially slower than the rate at which the lowerend of the buoy would descend it free from restraint to the tow vessel.

10. The method according to claim 6 including the step of removablyconnecting to at least one of the body sections at least one flotationtank prior to commencement of the towing step, and of removing theflotation tank prior to commencement of the sinking step.

References Cited UNITED STATES PATENTS 52,522 2/1866 Bowlsby 98 612,10910/1898 Hutchins 9-8 663,941 12/1900 Smith 9-8 2,473,618 6/ 1949Stillwagon 64-32 3,092,852 6/1963 Devereux 98 3,256,537 6/1966 Clark114-5 X FERGUS S. MIDDLETON, Primary Examiner. MILTON BUCHLER, Examiner.

T. MAJOR, Assistant Examiner.

